The present invention relates to a device and method for determination of the weight of a load that is linked to a working vehicle with the aid of a link device operable by a hydraulic cylinder so that the height of the load is variable. The device for weight determination includes a pressure sensor operating as a load-dependent sensor to determine the hydraulic pressure in the hydraulic cylinder and to generate a first signal depending on that hydraulic pressure and a position sensor to determine a position of the link device relative to the working vehicle and generate a second signal depending on that position.
A device for weight determination of a load is already known from German Patent Document DE 38 20 757, in which the weight of equipment connected to a tractor with an electro-hydraulic lifting device controller by means of an adjustable height 3-point link device is determined. A pressure sensor is used in this apparatus as load-dependent sensor for the weight determination. The pressure sensor measures the hydraulic pressure in a hydraulic cylinder used to raise and lower the load via the link device. In this type of device the center-of -mass position of the equipment, which could be a fertilizer spreader, for example, with material to be scattered, connected to the tractor by means of the lifting or link device is usually not known. Because of the torque that the weight exerts due to a displaced center of mass on the lifting device, a force must be applied by the hydraulic cylinder in general that supports both the force of the load and also the torque component due to the load. However the components are not separable from each other in the weight determination by measurement of the hydraulic cylinder pressure because of the unknown center of gravity position. This torque is obtained exclusively from the link members alone with the upper and lower link members of the link device in a parallel position. Because of this the link members in the link device start from a parallel position in the weight determination. The increase between the hydraulic cylinder pressure in the cylinder and a known empty weight of the attached equipment is determined by measuring the pressure in this position. The load weight is then determined with the aid of this value, however the link members must remain parallel during the measurement. However this is disadvantageous because the upper and lower link members of the link device are parallel only in a few cases when the equipment is connected in series with the link device so that the optimum prerequisites for weighing are not present in the tractor.
A device for weight determination of a load is also known from European Patent Document EP 0 496 869, in which a shovel or scoop is connected to the front side of a wheel loader by means of a hydraulic link device. A first signal of a pressure sensor arranged in a hydraulic cylinder and a second signal from a sensor detecting a position and/or geometry of the link device is used for weight determination, from which a correction value for the pitch of the working vehicle is determined and used for weight determination. It is disadvantageous that the pitch of the working vehicle is only derived in indirect form for weight determination so that high accuracy requirements are not fulfilled. Also calibrations with an empty shovel and with a predetermined load must be performed which increases the amount of work required for weight determination. An accurate calculation of the load is not possible in practice with this device, since approximation methods are used.